1. Field of the Invention
The present invention relates to a wireless IC device and, more particularly, to a wireless IC device that includes a wireless IC chip used for an RFID (Radio Frequency Identification) system.
2. Description of the Related Art
In recent years, an RFID system has been developed as an article management system, which includes a reader/writer that generates an induction field and an IC chip (also referred to as IC tag or wireless IC chip) that stores predetermined information allocated to an article or a casing, and non-contact communication is established between the reader/writer and the IC chip to transmit the information therebetween. A known existing wireless IC device equipped with an IC chip includes a non-contact IC medium module described in Japanese Unexamined Patent Application Publication No. 2003-331246.
The non-contact IC medium module is a combination of an LSI, a loop antenna and a capacitance element. The inductance of the line of the loop antenna and the capacitance of the capacitance element constitute a resonant circuit to carry out impedance matching between the loop antenna and the LSI.
However, in the non-contact IC medium module, in order to obtain an inductance value necessary for impedance matching with the LSI, it has been necessary to adjust the length of the loop antenna. Therefore, there has been a problem that the length of the loop antenna varies depending on the input impedance of an LSI used and, therefore, the size of the module itself and the antenna radiation characteristic vary.